Applied aspects of locomotion and biomechanics

Castro-Santos, T., Goerig, E., He, P., & Lauder, G. V. (2022). Applied aspects of locomotion and biomechanics. Fish Physiology, 39, 91–140. https://doi.org/10.1016/BS.FP.2022.04.003

Locomotion is the act and process of moving from place to place, which is fundamental to the life history of all mobile organisms. While the field of biomechanics encompasses the study of the physical constraints of what animals are capable of, ecological contexts require an integrated view that includes ecology and behavior. This chapter provides an overview of some of the areas where locomotion and biomechanics of fish movement interface with the rapidly evolving changes that humans impose on aquatic environments. These changes include fundamental alterations to the environment such as altered flows, fragmentation of riverine habitats, and invasive species, but also direct interactions that occur with capture fisheries. We explore each of these areas, considering both challenges and opportunities informed by the study of locomotion and biomechanics, emphasizing how this field can contribute to conservation of fishes in the Anthropocene. We then turn to technology, where important advances are aiding in our understanding of fish movement. In some cases those advances have themselves led to novel technologies, where biomimetic robots and related devices offer novel opportunities, both for conservation and for other pursuits. Read the full paper..

Unprecedented summer hypoxia in southern Cape Cod Bay: an ecological response to regional climate change?

Scully, M. E., Geyer, W. R., Borkman, D., Pugh, T. L., Costa, A., & Nichols, O. C. (2022). Unprecedented summer hypoxia in southern Cape Cod Bay: an ecological response to regional climate change? Biogeosciences, 19(14), 3523–3536. https://doi.org/10.5194/BG-19-3523-2022

In late summer 2019 and 2020 bottom waters in southern Cape Cod Bay (CCB) became depleted of dissolved oxygen (DO), with documented benthic mortality in both years. Hypoxic conditions formed in relatively shallow water where the strong seasonal thermocline intersected the sea floor, both limiting vertical mixing and concentrating biological oxygen demand (BOD) over a very thin bottom boundary layer. In both 2019 and 2020, anomalously high sub-surface phytoplankton blooms were observed, and the biomass from these blooms provided the fuel to deplete sub-pycnocline waters of DO. The increased chlorophyll fluorescence was accompanied by a corresponding decrease in sub-pycnocline nutrients, suggesting that prior to 2019 physical conditions were unfavorable for the utilization of these deep nutrients by the late-summer phytoplankton community. It is hypothesized that significant alteration of physical conditions in CCB during late summer, which is the result of regional climate change, has favored the recent increase in sub-surface phytoplankton production. These changes include rapidly warming waters and significant shifts in summer wind direction, both of which impact the intensity and vertical distribution of thermal stratification and vertical mixing within the water column. These changes in water column structure are not only more susceptible to hypoxia but also have significant implications for phytoplankton dynamics, potentially allowing for intense late-summer blooms of Karenia mikimotoi, a species new to the area. K. mikimotoi had not been detected in CCB or adjacent waters prior to 2017; however, increasing cell densities have been reported in subsequent years, consistent with a rapidly changing ecosystem. Read the full paper..

An interdisciplinary review of Atlantic Cod (Gadus morhua) stock structure in the Western North Atlantic Ocean

McBride, R. S. (editor), & Smedbol, R. K. (editor). (2022). An Interdisciplinary Review of Atlantic Cod (Gadus morhua) Stock Structure in the Western North Atlantic Ocean. https://doi.org/10.25923/SK1X-Z919

An Atlantic Cod Stock Structure Working Group (ACSSWG) was formed in early 2018 to inventory and summarize all relevant peer-review information about stock structure of Atlantic cod in US and adjacent waters (i.e., NAFO management divisions 5 and 6 and interactions with 4X). In addition, new data or information could be internally reviewed by the ACSSWG for inclusion in this report. Additional feedback was gained from 3 engagement sessions, 2 sponsored by New England Fishery Management Council and New Hampshire Sea Grant and 1 sponsored by the Maine Fishermen’s Forum, each of which added local ecological knowledge into the ACSSWG deliberations. Read the full paper..

A life history study of Atlantic Wolffish resolves bias and imprecision in length- and age-at-maturity schedules by recognizing abortive maturation

McBride, R. S., Fairchild, E. A., Press, Y. K., Elzey, S. P., Adams, C. F., & Bentzen, P. (2022). A Life History Study of Atlantic Wolffish Resolves Bias and Imprecision in Length- and Age-at-Maturity Schedules by Recognizing Abortive Maturation. Marine and Coastal Fisheries, 14(5), e10222. https://doi.org/10.1002/MCF2.10222

Stock assessments of U.S. Atlantic Wolffish Anarhichas lupus are hampered by a landings moratorium and low catches in fishery-independent surveys. Working with the commercial fishing industry, we collected hundreds of fish to overcome a lack of regionally specific life history information. Based on ages from sectioned otoliths, Atlantic Wolffish are long lived (maximum observed age: males = 31 years, females = 29 years). A Gompertz growth model showed that Atlantic Wolffish exhibit dimorphic growth—with larger males across all ages on average. Preliminary estimates of total mortality ranged from 0.15 to 0.21 and were lower than an estimate measured at the beginning of the moratorium. Based on gonad histology, a cohort of vitellogenic oocytes emerged in mature females by April and developed group synchronously to ovulate primarily in October. Skip spawning, which accounts for nonannual spawning, was observed in 5.6% of the mature females. Accounting for abortive maturation, a physiological event that delays functional maturation, improved precision and reduced bias of maturity estimates. The resulting median length at functional maturity was 53 cm total length (95% confidence interval = 49–56 cm), and the median age was 6.7 years old (6.2–7.2 years). These estimates are smaller and younger than elsewhere in the western North Atlantic Ocean, confirming that regionally specific maturity parameters are relevant when assessing reference points of the U.S. Atlantic Wolffish fishery. Read the full paper..

Evaluating growth dimorphism, maturation, and skip spawning of Atlantic halibut in the Gulf of Maine using a collaborative research approach

McBride, R. S., Maynard, G. A., Elzey, S. P., Hennen, D. R., Tholke, E. K., Runnebaum, J. M., & McGuire, C. H. (2022). Evaluating growth dimorphism, maturation, and skip spawning of Atlantic halibut in the Gulf of Maine using a collaborative research approach. Journal of Northwest Atlantic Fishery Science, 53, 57–77. https://doi.org/10.2960/J.V53.M736

The data-limited nature of Atlantic halibut (Hippoglossus hippoglossus) in U.S. waters hampers evaluation of what may be a slow but steady rebuilding pattern. Here, we collaborate with the commercial fishery to design and implement a multi-gear sampling program that collected 100s of biological samples from throughout the Gulf of Maine in a five-year period, 2014–2018. Examination of sectioned otoliths revealed a maximum age of 12 years (females) and 13 years (males); in comparison, Atlantic halibut as old as 40–50 years have been collected elsewhere in the western North Atlantic. Growth modeling confirmed sexual dimorphism, with a larger asymptotic length (L∞) for females (214 cm fork length [FL]) than males (195 cm FL). Estimates of median female length at maturity, L50, of 128 cm FL (124–132 cm, 95% confidence limits), and median female age at maturity, A50, of 9.6 years old (9.0–10.8 years), were longer and older than previous reports for the Gulf of Maine, likely resulting from our use of histological instead of macroscopic methods to classify maturity. Histology demonstrated that vitellogenesis initiated in individuals in spring, nearly a year prior to spawning, which allowed us to identify first-time (primiparous) spawners and provided the first potential evidence of skip spawning for this species. Finally, an index was developed to track the proportion of potentially mature females in the fishery, which showed an increasing trend; this qualitative tool may prove useful in a data-limited environment for evaluating the relative stock status of Atlantic halibut. Read the full paper..

Life history assessment of Cusk, a data-poor species, in U.S. waters

McElroy, W. D., Tholke, E. K., Wuenschel, M. J., & Robillard, E. (2022). Life History Assessment of Cusk, a Data-Poor Species, in U.S. Waters. Marine and Coastal Fisheries, 14(5), e10223. https://doi.org/10.1002/MCF2.10223

Cusk Brosme brosme are fished across the northern Atlantic Ocean, but even basic biological data are limited in part by their difficult-to-sample deep and structured habitats. We sampled fish from a variety of sources across the Gulf of Maine to provide comprehensive life history information (age and size at maturity, fecundity, sex ratio, growth) for this data-poor species considered by National Oceanic and Atmospheric Administration Fisheries as a species of concern. Gonad histology and gonadosomatic index data indicated peak spawning in late spring (May–June), with limited spawning activity into summer. The histologically derived length at 50% maturity for female Cusk was 39.5 cm TL. Fecundity varied from a quarter million to four million oocytes, with a positive allometry versus size indicating that larger females have proportionally higher fecundity than smaller females. Male Cusk had unusually low gonadal investment for a gadiform, and males of all sizes examined (down to 21 cm) had spermatozoa present. Male maturity was equivocal even when the relative proportions of sperm stages were quantified through image analysis of gonad histology; further anatomical and physiological studies of small males are required to assess functional maturity in male cusk. The sex ratio at length indicated more males at larger sizes, and males had faster growth and larger size at age than females. Condition patterns also suggested lower condition for females than males after spawning and generally less variable condition for males. Gonadal investment, relative condition, and growth patterns all suggest differences in energy allocation between the sexes. This data-poor species has an uncertain stock status in U.S. waters; therefore, the results of the current work provide important information to its management. Read the full paper..

Repeated targets of natural selection during ecological transitions of fish across salinity boundaries

Velotta, J., McCormick, S., Whitehead, A., Durso, C., & Schultz, E. (2022). Repeated Targets of Natural Selection during Ecological Transitions of Fish Across Salinity Boundaries. EEB Articles. https://opencommons.uconn.edu/eeb_articles/52

Ecological transitions across salinity boundaries have led to some of the most important diversification events in the animal kingdom, especially among fishes. Adaptations accompanying such transitions include changes in morphology, diet, whole-organism performance, and osmoregulatory function, which may be particularly prominent since divergent salinity regimes make opposing demands on systems that maintain ion and water balance. Research in the last decade has focused on the genetic targets underlying such adaptations, most notably by comparing populations of species that are distributed across salinity boundaries. Here, we synthesize research on the targets of natural selection using whole-genome approaches, with a particular emphasis on the osmoregulatory system. Given the complex, integrated and polygenic nature of this system, we expected that signatures of natural selection would span numerous genes across functional levels of osmoregulation, especially salinity sensing, hormonal control, and cellular ion exchange mechanisms. We find support for this prediction: genes coding for V-type, Ca2+, and Na+/K+-ATPases, which are key cellular ion exchange enzymes, are especially common targets of selection in species from six orders of fishes. This indicates that while polygenic selection contributes to adaptation across salinity boundaries, changes in ATPase enzymes may be of particular importance in supporting such transitions. Read the full paper..

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